1. Field of the Invention
The present invention relates to a fuel supplying apparatus used for an in-cylinder injection type internal combustion engine, and more particularly, to a fuel supplying apparatus which permits minimization of pulsation width of the fuel pressure, stabilizes the quantity of injected fuel and makes it possible to stabilize the engine revolutions.
2. Description of the Related Art
As an internal combustion engine of a type injecting a fuel into cylinders of the engine, referred to as the in-cylinder injecting type internal combustion engine or the direct injecting type internal combustion engine, there is widely known a diesel engine. An in-cylinder injecting type engine has recently been proposed even for a spark igniting engine (gasoline engine). In such an in-cylinder injecting type internal combustion engine, there is a tendency toward increasing the fuel injecting pressure to achieve finer fuel atomizing, and reducing the fuel injecting period. In an engine provided with a supercharging mechanism, a high fuel injecting pressure meeting the supercharging pressure is required upon supercharging. In a fuel supplying system in an in-cylinder injecting type internal combustion engine, therefore, it is a common practice to achieve a sufficiently high fuel injecting pressure of, for example, 10 atm.
FIG. 14 is a schematic configuration diagram illustrating a conventional fuel supplying apparatus. In FIG. 14, a delivery pipe 1 has injectors 1a corresponding to the number of cylinders of an engine not shown. A high-pressure fuel pump 3 is arranged between the delivery pipe 1 and the fuel tank 2. The delivery pipe 1 and the high-pressure fuel pump 3 are connected by a high-pressure fuel path 4. The high-pressure fuel pump 3 and the fuel tank 2 are connected by a low-pressure fuel path 5. A filter 6 is provided at a fuel inlet port of the high-pressure fuel pump 3. A check valve 7 is provided on the discharge side of the high-pressure fuel pump 3. A drain 8 of the high-pressure fuel pump 3 is brought back to the fuel tank 2. The high-pressure fuel pump 3, the filter 6 and the check valve 7 are integrally formed as a high-pressure fuel pump 100.
A low-pressure fuel pump 10 is provided at the end of the low-pressure fuel path 5 on the side thereof facing the fuel tank 2. A filter 11 is provided at a fuel inlet port of the low-pressure fuel pump 10. A check valve 12 is provided in the low-pressure fuel path 5 on the discharge side of the low-pressure fuel pump 10. A low-pressure regulator 14 is provided in the low-pressure fuel path 5 between the high-pressure fuel pump 3 and the low-pressure fuel pump 10. A filter 15 is provided at a fuel inlet port of the low-pressure regulator 14. A drain 16 of the low-pressure regulator 14 is returned to the fuel tank 2.
The delivery pipe 1 has a further high-pressure fuel path 18 on the side opposite to the high-pressure fuel pump 3. A high-pressure regulator 20 is provided in this high-pressure fuel path 18. A drain 21 of the high-pressure regulator 20 is brought back to the fuel tank 2. The high-pressure regulator 20 is composed as a high-pressure regulator unit 110, and is installed at a prescribed position between the delivery pipe 1 and the fuel tank 2.
A fuel pressure sensor 22 is provided in the high-pressure fuel path 4.
In the fuel supplying apparatus having a configuration as described above, a fuel pressurized to some extent in the low-pressure fuel pump 10 is further pressurized in the high-pressure fuel pump 3, reaches the delivery pipe 1, and injected from the injector 1a into cylinders of an engine not shown. At this point, the discharge pressure from the low-pressure fuel pump 10 is stabilized within a prescribed range by the low-pressure regulator 14, and the discharge pressure from the high-pressure fuel pump 3 is stabilized within a prescribed range by the high-pressure regulator 20.
In the fuel supplying apparatus of this configuration, however, the discharge pressure of the fuel discharged from the high-pressure fuel pump 3 suffers a large pulsation. This pulsation is reflected to the high-pressure regulator 20, and a part thereof goes back on the high-pressure fuel pump 3 side, where it is enlarged further through resonance. More specifically, in the high-pressure fuel path 4 between the high-pressure fuel pump 3 and the high-pressure regulator 20, the delivery pipe 1 and the high-pressure fuel path 18, the pulsation produced in the high-pressure fuel pump 3 is enlarged through resonance with the reflected wave. This pulsation causes a variation of the quantity of fuel injected from the delivery pipe 1. This variation of the quantity of injected fuel causes an unstable air/fuel ratio, and unstable revolutions of the engine. Pulsation of fuel in the piping causes another problem of occurrence of abnormal sound. Particularly, when the high-pressure fuel pump 3 is of the single-cylinder type, this serious pulsation poses a difficult problem.